The invention relates to vascular repair devices, and in particular intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery.
Stents are generally tubular-shaped devices that hold open a segment of a blood vessel or other body lumen such as a coronary artery. They also are suitable to support and hold back a dissected arterial lining that can occlude the fluid passageway. There are many known stents, such as those disclosed in U.S. Pat. No. 6,629,994, entitled “Intravascular Stent” and issued on Oct. 7, 2003, which is incorporated by reference herein.
The prior art stents depicted in FIGS. 1-5 have multiplex cylindrical rings connected by one or more undulating links. While some of these stents are flexible and have the appropriate radial rigidity needed to hold open a vessel or artery, there typically is a tradeoff between flexibility, radial strength, and the ability to tightly compress or crimp the stent onto a catheter. Crimping the stent is important so that it does not move relative to the catheter or dislodge prematurely prior to controlled implantation in a vessel.
In these prior art stents, each of the cylindrical rings making up the stent has proximal and distal ends, and a cylindrical plane defined by a cylindrical outer wall surface that extends circumferentially between the proximal end and the distal end of the cylindrical ring. Generally, the cylindrical rings have a serpentine or undulating shape that includes one or more U-shaped elements. The cylindrical rings are interconnected by at least one undulating link that attaches one cylindrical ring to an adjacent cylindrical ring.
The undulating links may take various configurations but, in general, have an undulating or serpentine shape. The undulating links can include bends connected by substantially straight portions wherein the substantially straight portions are substantially perpendicular to the stent longitudinal axis.
The cylindrical rings typically are formed of a plurality of peaks and valleys, where the valleys of one cylindrical ring are circumferentially offset from the valleys of an adjacent cylindrical ring. In this configuration, at least one undulating link attaches each cylindrical ring to an adjacent cylindrical ring so that at least a portion of the undulating links is positioned within one of the valleys and it attaches the valley to an adjacent peak.
While the cylindrical rings and undulating links generally are not separate structures, they have been conveniently referred to as rings and links for ease of identification. Further, the cylindrical rings can often be thought of as comprising a series of U's, W's and other-shaped structures in a repeating pattern. Again, while the cylindrical rings are not divided up or segmented into U's, W's and other shapes, the pattern of the cylindrical rings resemble such configuration. The U's, W's and other shapes promote flexibility in the stent primarily by flexing and by tipping radially outwardly as the stent is delivered through a tortuous vessel.
Although there are many advantages to stents of this type, recent advances in stent design in which the stent is coated with drugs, raise new design challenges. It is important that as the stent is crimped prior to insertion into the body, there is no contact between portions of the stent. This type of contact, as illustrated in FIGS. 6 and 7, can have adverse effects on the drug coating which can, for example, form a bubble and peel off.
What is needed is a flexible and strong stent having very little or no contact between structural members as the stent is crimped prior to insertion into the body. It is also desirable to increase the coatability of the stent, to reduce flaring, and/or to improve stent retention.